According to this site, Free allows credit cards and now you can cancel without fines:

Quote:

Free Mobile mobile is a Pay as You Go program, with automatic renewals, but no fines for canceling early, no activation fees, etc. All credit/debit cards, not limited to French issued ones, should function fine. (Automatic payment via a French bank account is also possible.)

[Under 'paiement de votre commande' on the right hand side, under the box there is a link which says payer par carte bancaire. It will then change the box to one that allows you to enter the details of any card. Your bank may charge a transaction fee for using this.]